infrastructure. Instead, the existing extent of barbed wire fences could be used to transmit electric signals and connect telephones in neighboring farms. In 1902, The New York Times reported that ranchers in Montana were instituting a telephone exchange in Fort Benton with the goal of eventually connecting every city in the state. The main purpose of such networks was to transmit weather conditions and forecasts, as well as train schedules. Railroad systems Telephone service for dispatchers and service personnel between way stations along railways used a form of party line service for many decades starting in the early 1900s. Railroad telephone systems often consisted of several dozen way stations interconnected with a shared line that used DC voltages as high as 400 V for selective signaling to alert called stations. Carrier systems With the advent of sophisticated electronics, telephone service providers developed methods to share a single copper line to transmit multiple telephone calls simultaneously. Various pair gain methods using time-division multiplexing and frequency-division multiplexing prevented interference between simultaneous calls. A distant suburb may have a subscriber loop carrier or digital loop carrier system in which a remote concentrator is located near the subscribers to connect multiple local subscriber loops to one common line to a central office exchange. A single optical fibre can also be shared between multiple subscribers in fibre to the cabinet systems. CATV cable modems are connected to an inherently shared medium. The signal from the shared line is split to multiple subscribers. Signals for television, and data operate at various different carrier frequencies. Digital wireless connections, such as mobile phones or voice over IP running over rural wireless Internet infrastructure are also inherently a shared medium. Sufficiently high levels of usage of simultaneous active connections cause congestion on a mobile telephone network or impair transmission quality. Modern usage Party lines are still in use primarily in rural areas where local loops are long and individual circuits are uneconomical when spread sparsely over a large area. Privacy is limited and congestion often occurs. In isolated communities, party lines have been used for local service only, without the facilities to switch calls through a central office for connection to the public switched telephone network. An example of a community linked by a party line is in Big Santa Anita Canyon high in the mountains above Los Angeles, near Sierra Madre, California. A group camp, a pack station